Disturbed intestinal epithelial cell homeostasis is a key feature of inflammatory bowel disease (IBD). Multiple studies have reported mitochondrial dysfunction in epithelial cells during IBD. Damaged mitochondria are a key source of increased intracellular reactive oxygen species (ROS) from respiratory chain dysfunction that can result in cell death. Expression of prohibitin (PHB), a mitochondrial protein, is decreased in mucosal biopsies from IBD patients and in animal models of colitis. Our previous studies have shown that restoration of colonic epithelial PHB expression using genetic manipulation (villin-PHB transgenic mice) or therapeutic delivery to the colon via nanoparticle or adenovirus protects mice from experimental colitis and reduces oxidative stress. Gene silencing of PHB in cultured intestinal epithelial cells increases mitochondrial membrane depolarization, intracellular ROS, mitophagy, and apoptosis, suggesting that PHB is involved in maintaining mitochondrial integrity and epithelial cell homeostasis. Furthermore, our recent data show that PHB interacts with STAT3 in colon mucosa and cultured intestinal epithelial cell lines and modulates its downstream apoptotic responses. In addition to its activities as a transcription factor, STAT3 has recently been shown to reside in the mitochondria of cells and promote optimal electron transport chain activity. Based on these data, the central hypothesis of this proposal is that PHB modulates mitochondrial STAT3 to maintain mitochondrial integrity and homeostasis in intestinal epithelial cells. To address this hypothesis, the following Aims will be tested: 1) to characterize PHB-mediated mitochondrial STAT3 modulation and its downstream effects on apoptosis and mitochondrial function and 2) to use an intestinal epithelial cell-specific PHB conditional knockout mouse as an in vivo model for examining the role of PHB in maintaining intestinal epithelium homeostasis and modulating mitochondrial STAT3 during basal conditions and colitis. The overall objective of this proposal integrated across the two Aims is to determine the role of PHB in maintaining epithelial homeostasis and mucosal integrity. Together, these studies will provide novel comprehensive data on the involvement of PHB and STAT3 in mitochondrial dysfunction characteristic of intestinal inflammation. We believe our findings will identify novel molecular mechanisms that act to preserve epithelial barrier integrity basally and in the context of tissue injury and will provide new therapeutic targets.